Magnetically coupled radio frequency identification (“RFID”) technology allows data acquisition or transmission from and to active (e.g., battery-powered, -assisted, or -supported) or passive RFID transponders using RF magnetic induction. To read or write to a transponder or a memory element of a transponder, the transponder is exposed to an RF magnetic field that couples with and may energize the RFID transponder through magnetic induction and transfers commands and data from a reader using a predefined “air interface” RF signaling protocol.
When multiple transponders are within the range of the same RF magnetic field they may each be energized and attempt to communicate with the transceiver, potentially causing errors in reading or writing to a specific transponder, often referred to as collision errors. Anti-collision management technologies exist to allow near simultaneous reading and writing to numerous transponders in a common RF magnetic field. However, anti-collision management increases system complexity, interrogation time, and cost. Furthermore, anti-collision management is blind, i.e., it cannot determine what transponder or transponders are responding out of a plurality of transponders near the antenna of the reader.
One way to prevent errors during reading and writing to particular transponder without using anti-collision management is to isolate that transponder from the nearby or adjacent transponders. For example, devices or systems may employ an RF-shielded housing or anechoic chamber for shielding a targeted transponder from the other transponders. The transponders are individually passed though the shielded housing or chamber for individualized exposure to an interrogating RF magnetic field. Unfortunately, RF-shielded housings add cost and complexity to a system. Furthermore, many systems are limited with regard to space or weight and, thus, cannot accommodate such shielded housings.
When transponders are supplied attached to a carrier substrate, e.g., RFID-mounted labels, tickets, tags or other media supplied in bulk rolls, Z-folded stacks or other format, an extra portion of the carrier substrate is required to allow one transponder on the carrier substrate to exit the shielded field area before the next transponder in line enters it. The extra carrier substrate increases materials costs and the required volume of the RFID media bulk supply for a given number of transponders. Also, the increased spacing between transponders may also slow overall throughput of the system.
When the size or form factor of the utilized transponder is changed, the RF shielding and or anechoic chamber configuration may also require reconfiguration, adding cost and complexity and reducing overall productivity.
There are applications in which it is desired to print on transponder-mounting media in the same target space in which the transponder is being read from or written to (e.g., printer-encoders). This may be difficult to accomplish if the transponder must be interrogated in a shielded housing or chamber.
Printer-encoders have been developed which are capable of on-demand printing on labels, tickets, tags, cards or other media that include a transponder (often referred to as “smart media”). These printer-encoders have an RFID transceiver for on-demand communicating with the transponder of the individual media. For the reasons given, it may be desirable in some applications to present the smart media on rolls or other formats in which the transponders are closely spaced. However, as explained above, the close space between the transponders may exacerbate the task of serially communicating with each individual transponder without concurrently communicating with transponders on neighboring media. The selective communication of an individual transponder among a plurality of closely spaced transponders may be further exacerbated in printer-encoders (or other conveyor systems) configured to print on the media in the same space as the transponder is positioned when being interrogated.